A semiconductor device including a drive circuit such as a solenoid load to be mounted in an in-vehicle electrical control unit (ECU) is required to have a high breakdown voltage of equal to or higher than 30 V and a current drive ability with high ampere order and to absorb current energy generated at an output terminal so as not to cause malfunction and destruction of an element of a power transistor. Therefore, there is a method of providing active clamp circuits at a gate and a drain of a power transistor of an output stage (for example, refer to PTL 1). As a result, the current energy generated at the output terminal can be discharged to the ground.
Here, current energy (thermal breakdown energy) which can be consumed by a power transistor at the time of an active clamping operation is determined based on an occurrence condition of thermal runaway caused by self-heating of the transistor, and the value of the current energy can be increased by increasing a size of the transistor in general. However, there is a problem such that the increase in the size of the transistor increases chip cost.
On the other hand, in a relatively large power transistor, since heat dissipation properties of a center region and a peripheral region are different from each other, temperatures of the center region and the peripheral region are different from each other. That is, although the temperature is high in the center region with poor heat dissipation properties, the temperature is low in the peripheral region due to the heat dissipation effect. As a result, there are problems such that the thermal breakdown energy of the transistor cannot be increased by a corresponding amount and that the amount of the allowable energy is restricted to be small and the use environment temperature of the transistor cannot be set to be high so that the junction temperature of the transistor does not exceed the rated temperature from the viewpoint of reliability.
To solve these problems, techniques are disclosed for uniforming the temperature distribution in the transistor. One of the techniques is a method in which intervals between active regions of transistors arranged in parallel are widened in the center region and are narrowed in the peripheral region (for example, refer to PTL 2), and another method is a method of reducing an input power in the center region to be lower than an input power in the peripheral region. In either method, the temperature distribution in the transistor can be uniformed by decreasing the power consumption per unit area from the peripheral region toward the center region, and as a result, the thermal breakdown energy of the transistor can be increased.
Furthermore, a technique is disclosed in which a non-active region is provided in the center region of the power transistor and a heat radiation electrode is formed on the non-active region (for example, refer to PTL 3). By deactivating the center region where the temperature rises, the temperature in the transistor can be reduced, and the uniformity of the temperature can be enhanced. Furthermore, the temperature can be further lowered by radiating heat to the outside of a semiconductor via the heat radiation electrode. As a result, the thermal breakdown energy of the transistor can be increased.
Furthermore, a technique is disclosed in which, in a semiconductor integrated circuit having an overtemperature detection circuit for detecting whether the temperature of the power transistor is equal to or higher than a predetermined temperature, when the temperature of the transistor becomes equal to or higher than the predetermined temperature, the transistor is not driven, and the power transistor is set to be an active clamp state with a second clamp voltage lower than a first clamp voltage (for example, refer to PTL 4). Since it is possible to suppress a rapid increase in the temperature of the transistor by lengthening a time when surge energy is consumed, temperature setting for detecting an overtemperature can be closer to the maximum operation guarantee temperature. As a result, the transistor can be operated at a higher temperature.